Titanium pigment and process for producing the same



Patented Aug. 27, 1940 UNITED STATES PATENT OFFICE I ITANIUM PIGMENT ANDPROCESS FOR PRODUCING THE SAME No Drawing. Application April 8, 1938,Serial No. 200,912

10 Claims.

adversely affect the utility of such pigments.

It is among the objects of this invention, to overcome theseobjectionable features in' prior titanium pigments, and to provide atreated and improved titanium pigment which is remarkably stable andresistant against weathering, discoloration, chalking, or lack of tintretention.

A further and particular object of the invention includes the productionof a titanium pigment which is substantially free from soluble salts,and the provision of a process for treating titanium pigmentswhicheliminates and avoids the introduction of soluble salts into the pigmentduring treatment. This is very advantageous because the adsorptivenature of the pigment is such that soluble salts cannot be completelyremoved by washing, and, unless present only to a negligible extent,exert a severe and'adverse effect upon the durability characteristics ofexterior paints and coating compositions in which the pigment may beemployed.

The foregoing objects and advantages, as well as others, are obtainablein the present invention, which broadly comprises subjecting a titaniumpigment to treatment with an insoluble aluminum compound by reactingaluminum sulfate with a compound of a metal, the sulfate of which iswater-insoluble or only sparingly soluble.

In a more specific and preferred embodiment, the invention comprisesadding aluminum sulfate to a water slurry of calcined titanium oxide,and precipitating the aluminum on the pigment in the form of a hydratedoxide by addition of an alkaline earth metal hydroxide. according to theIn one preferred adaptation, a solution of 55 aluminum sulfate is addedto a water slurry of obviously very objectionable and, seriously and thetitanium pigment during agitation. The pH of the slurry is graduallyadjusted to neutralization by addition, during vigorous stirring, of asuitable quantity of an alkaline earth metal hydroxide solution,preferably barium hydroxide. Neutralization and addition of thehydroxide induces precipitation of the aluminum on the pigment in theform of insoluble aluminum hydrate. The slurry is then filtered, thepigment dried and ground, and is then ready for use.

In order that the invention may be more clearly understood, thefollowing specific examples are given, each of which is merelyillustrative in character:

Example I 30,360 parts by weight of a calcined, wet ground titaniumoxide slurry containing 9080 parts by weight of titanium oxide wasdiluted with suiiicient water to permit eflicient stirring, the titaniumoxide concentration then being about 20% by weight of the slurry. Tothis slurry was then added 593 parts by weight of A12(SO4)3.18H2Odissolved in about two thousand parts of water which represents anamount of aluminum equivalent to 1% aluminum oxide on the basis of thetitanium oxide. After thorough stirring to insure uniform mixing of thealuminum sulfate solution with the pigment, aqueous barium hydroxidesolution was slowly added with vigorous stirring to the slurry. Additionof barium hydroxide was continued until the slurry had a pH 7.0 to 7.2.The slurry was then filtered and the pigment dried, after which it wasdry ground and was then ready for use.

The resultant pigment was formulated in a baking enamel based on adrying oil modified one hour at 260 F. A second coat was applied andbaked in the same manner. For comparative purposes an enamel wasprepared in the same manner but pigmented with untreated titanium oxide.These panels were placed on indoor exposure in a well lighted room andafter 16 months exposurethe panel coated with the enamel containinguntreated TiOz had discolored badly whereas the composition containingthe treated TiOz exhibited very good color retention. These panels weregraded on an arbitrary scale'in which one unit represented a distinctvisual color difference. On this scale the composition containity ofapproximately 17 units over the similar composition pigmented withuntreated titanium oxide.

Example II 500 parts by weight of finished, dry titanium oxide wasslurried in 1750 parts by weight of water and ground in a colloid millto eliminate aggregated material. 21.3 parts by weight ofAl2(SO4)s.18H2O was dissolved in 200 parts by weight H20 and added tothe slurry with vigorous stirring. The slurry was then neutralized to apH of 7.0 by gradually adding a dilute suspension of calcium hydroxideto the slurry. The calcium hydroxide slurry was added very slowly andwith good agitation to avoid the possibility of any free calciumhydroxide remaining with the pigment. The slurry was then filtered andthe pigment dried. The amount of aluminum added was equivalent to 0.65%aluminum oxide on the basis of the titanium oxide content.

The resultant pigment, when incorporated in an exterior paintformulation and exposed to weathering for a period of two months on atest panel, exhibited no tendency towards chalking, discoloration orlack; of tint retention. On the other hand, a similar but untreatedpigment, when incorporated in a like paint formulation, and subjected toa like test chalked and discolored badly within a period of a week andexhibited a marked lack of tint retention.

While in the foregoing examples, a solution of barium hydroxide and asuspension of calcium hydroxide have been employed, it will be apparentthat solutions or suspensions of strontium hydroxide may also beemployed. Similarly, while in the preferred adaptation of our invention,the hydroxides of these metals are utilized, other alkaline earth metalcompounds which form insoluble sulfates may also be used, such as bariumcarbonate, calcium carbonate, or strontium carbonate, etc.

It will be seen that the invention can be applied to the treatment of adry finished titanium oxide pigment which has been slurried in water orthe pigment may be treated at any convenient point in the process, aftercalcination. In titanium oxide pigment manufacture, the pigment isusually dispersed and wet ground after calcination. The treatment may beapplied to this dispersed material or it can be equally well applied tothe fiocculated pigment during or at any point in the finishing process.Similarly, pigment treatment may be effected by separately precipitatingand subsequently blending the agent with the pigment, preferably whilein aqueous slurry.

In the preferred practice of the invention, it will be found thatrelatively small and minor amounts of hydrated aluminum oxide need beapplied to the pigments and that in most instances it will beundesirable and unnecessary to employ in excess of substantially 2%,expressed as aluminum oxide and based on the weight of the pigment.Usually, about 1% of agent will be found sumoient, although in theobtainment of maximum effectiveness and pigments of consistently uniformsuperiority, we preferably employ amounts ranging from substantially.02% to 1.5%, calculated as added aluminum oxide; The employment of thislow range, in addition to affording desired effectiveness, maintains thetitanium oxide content of the pigment desirably high and avoids anyunnecesing the pigment of Example I showed a superiorsary dilution ofthe pigment with consequent sacrifice in covering power and otheressential pigmentary properties. We have found that treatments withamounts of reagent equivalent to about 0.3% to 0.5% aluminum oxide arealso particularly and desirably effective; that when a pigment istreated with an amount of agent equivalent to 0.15% aluminum oxide, itexhibits marked advantages over an untreated pigment as regardschalk-resistant properties and resistance to discoloration in the light,particularly when used in an enamel based on a drying oil modifiedpolyhydric alcohol-polybasic acid resin vehicle.

Exposures of enamels formulated with our treated pigments have been madeand the data are given hereunder in Table I. In these tests the treatedtitanium oxide was the sole pigment and the vehicle was a polyhydricalcohol-polybasic acid enamel of the type used in the manufacture ofwhite interior finishes. The panels were spray coated and the dried filmexposed to diffuse daylight in the laboratory with half of the rpanelcovered so as to note differential yellowing between the two portions.

After three months the films were measured In the above table thedominant wave length and excitation purity for both the exposed and theunexposed portions are given. The excitation purity is a measure of thedeviation of a near white from a neutral white in the direction of thedominant wave length. (See Handbook of Colorimetry by ,A. C. Hardy,Technology Press, Mass. Institute of Technology, 1936, page 12. Thehigher of value for excitation purity the greater the deviation fromneutral white, or, in the case under consideration, the more yellow thefilm.

It will be noted that the exposed enamels made my treated pigment,whereas the exposed portion is quite yellow in the case of the untreatedpigment.

Accordingly, the c mposition of our improved titanium pigment willcomprise titanium dioxide or other titanium pigment, with which isassociated not more than substantially 2% of hydrated aluminum oxide,calculated as aluminum oxide, and the corresponding chemicallyequivalent amount of alkaline earth metal sulfate. For example, theadded hydrated aluminum oxide, calculated as the oxide in the pigment,may range from about .02% to 2%, and the alkaline earth metal sulfatemay range from strength and hidingpower is afforded, the titaniumdioxide content of which may range as high as 92% or higher, equallingin effect a 100% product.

The treated pigments may be used in the same manner as the untreatedpigments for indoor and outdoor coating composition formulations. Thesepigments have particular value in white or light colored enamelsdesigned principally for indoor use where yellowing in the light is mostapparent and consequently a distinct fault. Such compositions formulatedwith untreated titanium oxide show a gradual color change on exposure tothe light which is usually yellowish, yellowish brown, or even reddishbrown. In certain compositions this color change is so severe thattitanium oxide cannot be used as a pigment and other lower hidingpigments must be used in lieu thereof, which is a distinct disadvantage.By the use of the treated pigments of the present invention, suchcompositions exhibit a very marked improvement in color stability,weathering and chalk-resistance.

The results of actual exposure tests have proven that the new pigment,when incorporated in cellulose nitrate vehicles, affords a highlychalkre'sistant finish, a result which is quite unexpected in view ofthe known deleterious chalking tendencies of cellulose nitrate typefinishes which contain untreatedtitanium dioxide. The noteworthyimprovements in chalk-resistance afforded in the use of the new pigmentare apparent in the conventional cellulose nitrate vehicles wherenatural resins, softeners and plasticizers are present as essentialingredientsyas well as in the more recently developed type of cellulosenitrate composition which includes appreciable proportions of syntheticresins, for example, a modified alkyd type resin.

'As stated, the introduction or addition of soluble salts into thepigment adversely affects the durability qualities of paints and coatingcompositions, particularly those employed in exterior compositions. Dueto the adsorptive'nature of the pigment, soluble salts cannot becompletely removed by washing or other known treatments, and. if presentin the pigment in an amount up to substantially .25%, will not seriouslyimpair its pigmentary properties. Such amount is relatively minor andnegligible in extent and is unavoidably present in the pigment as aresult of normal processing and as an impurity introduced from materialsemployed in pigment production. Accordingly, it will be seen that thetreated pigment of the present invention is substantially free from andcontains less than substantially 25% of water-soluble salts, thusproviding an "improved pigment which when incorporated in outside paintsor coating compositions insures maximum film durability. A furtheradvantage ofthe invention lies in the elimination of unde- "s'iredafter-treatment and thus affords a very definite process simplification.This is particularly important in the production of pigments on a plantscale, since our treatment may be applied to a water slurry of thefinished pigment .Wlllh an absolute minimum of additional equipment andby a simple additional process step which is very economical from thestandpoint of operation.

The treatment provided for may be applied to all types of titaniumpigments, the term titanium pigment, here and in the appended claims,being meant to include titanium oxide, titanium oxide chemicallycombined with other metal oxides, such as the titanates of magnesium,calcium, strontium, barium, zinc, and cadmium, etc., as well as titaniumpigments associated with extenders such as the alkaline earth metalsulfates of calcium and barium, as well as silica, magnesium silicateand silicates in general.

. We claim as our invention:

1. A process for producing a non-reactive, calcined. stable,weather-resistant titanium oxide pigment, substantially free of solublesalts comprising adding a predetermined amount of aluminum sulfate to asuspension of said pigment and precipitating from about .02% to not morethan about. 2% of an insoluble aluminum compound thereon, calculated asA1203, by reacting said sulfate with a compound from the groupconsisting of alkaline earth metal hydroxides and carbonates.

2. A process for producing a non-reactive, calcined, stable,weather-resistant titanium pigment substantially free of soluble saltscomprising adding aluminum sulfate to a suspension of said pigment andprecipitating not in excess of 2%, calculated as A1203, of an insolublealuminum compound thereon by reacting said sulfate with an alkalineearth metal hydroxide.

3. A process for producing a non-reactive, calcined, stable,weather-resistant titanium pig-- ment substantially free of solublesalts'comprising adding aluminum sulfate to a suspension of said pigmentand precipitating not to exceed 2%, calculated as A1203, of an'insolublealuminum compound thereon by reacting said sulfate with an alkalineearth metal carbonate.

4. A process for producing a non-reactive, calcined, stable,weather-resistant titanium pigment substantially free of soluble saltscomprising adding aluminum sulfate to a water slurry of said pigment andprecipitating not in excess of 2%, calculated as A1203, of hydratedaluminum oxide thereon by reacting said sulfate with an alkaline earthmetal hydroxide.

5. A process for producing a non-reactive, calcined, stable,weather-resistant titanium pigment, substantially free of soluble saltscomprising adding aluminum sulfate to a water slurry of titaniumdioxide, and precipitating not in excess of 2%. calculated as A1203, ofhydrated aluminum oxide thereon by reacting said sulfate with bariumhydroxide.

6. A process for producing a non-reactive, calpenslon of said pigment toprecipitate an amount of aluminum hydroxide ranging from .02% to 1.5%,calculated as A1203, on said pigment by reacting said sulfate with analkaline earth metal hydroxide.

7. A process for producing a non-reactive, calcined, stable,weather-resistant titanium pigment substantially free of soluble saltscomprising adding sumcient aluminum sulfate to a suspension of saidpigment to precipitate an amount of aluminum hydroxide, calculated asA1203, ranging from .02% to 1.5% on said pigment by reacting saidsulfate with barium hydroxide.

8. A process for producing a non-reactive, stable, calcined titaniumpigment substantially free of soluble salts, comprising reacting, in thepresence of said titanium pigment, a predetermined amount of aluminumsulfate with a predetermined amount of a compound from the groupconsisting of alkaline earth metal hydroxides and carbonates, wherebyfrom about .02% to not tive, calcined, stable, weather-resistanttitanium pigment substantially free of soluble salts havingco-precipitated thereon from about 0.3% to not more than substantially1.5% of hydrated aluminum oxide, calculated as A1203, and fromsubstantially 2% to 10% of barium sulfate.

MARION L. HANAHAN. ROBERT M. MCKINNEY.

